An emergency has been declared at a nuclear facility in the United States after a tunnel containing rail cars full of nuclear waste collapsed.

Workers evacuated or took cover and turned off ventilation systems after minor damage was discovered in the wall of a transport tunnel – a spokeswoman for the Department of Energy said.The damage was more serious than initially reported and the take-cover order was expanded to cover the entire facility after response crews found a 400-square-foot section of the decommissioned rail tunnel had collapsed- she said.